Cellstructure& Genetic Control
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  • 1. Cell Structure and Genetic Control www.freelivedoctor.com
  • 2. Cell
    • Basic unit of structure and function of the body.
      • Highly organized molecular factory.
    • Great diversity of function.
      • Organ physiology derived from complex functions of the cell.
    • 3 principal parts:
      • Plasma membrane.
      • Cytoplasm and organelles.
      • Nucleus.
    www.freelivedoctor.com
  • 3. Plasma Membrane
    • Is selectively permeable .
    • Composition:
      • Double layer of phospholipids due to hydrophobic/hydrophilic parts.
        • Restrict passage of H 2 0 and H 2 0 soluble ions.
      • Proteins span or partially span the membrane .
        • Provide structural support, transport molecules, serve as receptors.
      • Negatively charged carbohydrates attach to the outer surface.
        • Involved with regulatory molecules.
    www.freelivedoctor.com
  • 4. Plasma Membrane (continued) www.freelivedoctor.com
  • 5. Cytoplasm, Organelles, Nucleoli
    • Cytoplasm:
      • Aqueous content of the cell.
    • Organelles:
      • Sub-cellular structures within the cytoplasm.
    • Nucleus:
      • Is a large spheroid body.
      • Largest of the organelles.
      • Contains the genetic material (DNA).
      • Nucleoli:
        • Centers for production of ribosomes.
    www.freelivedoctor.com
  • 6. Cytoplasm, Organelles, Nucleoli (continued) www.freelivedoctor.com
  • 7. Bulk Transport
    • Phagocytosis:
      • Phagocytic cells use pseudopods to surround and engulf particles.
      • Pseudopods join, fuse, and surround ingested particle (food vacuole).
        • Lysosomes digest food vacuole.
      • Protects from invading organisms.
      • Removes debris.
    • Endocytosis:
      • Pinocytosis:
        • Nonspecific process.
        • Plasma membrane invaginates, fuses, vesicle containing ECF pinches off, and vesicle enters cell.
    www.freelivedoctor.com
  • 8. Bulk Transport (continued)
    • Receptor-mediated endocytosis:
      • Interaction of molecules in ECF with specific membrane receptor proteins.
      • Membrane invaginates, fuses, pinches off and forms vesicle.
      • Vesicle enters cell.
    • Exocytosis:
      • Process by which cellular products are secreted into extracellular environment.
      • Proteins and other molecules to be secreted are packaged in vesicles by Golgi complex.
      • Vesicles fuse with plasma membrane and release contents into extracellular environment.
    www.freelivedoctor.com
  • 9. Cilia, Flagella, Microvilli
    • Cilia:
      • Tiny hair-like structures that project from the surface of the cell.
        • Stroke in unison.
          • Respiratory tract, uterine tube.
    • Flagella:
      • Simple whip-like structure that propels sperm through its environment.
    • Microvilli:
      • Numerous folds (finger-like projections) increase surface area.
        • Aid absorption.
    www.freelivedoctor.com
  • 10. Cytoplasm and Cytoskeleton
    • Cytoplasm:
      • Jelly-like matrix within the cell.
      • Includes organelles and cytosol.
      • Highly organized structure with microtubules and microfilaments that function as cytoskeleton.
    • Cytoskeleton:
      • Actin and myosin (microfilaments).
      • Spindle apparatus (microtubules).
    www.freelivedoctor.com
  • 11. Lysosomes
      • Primary:
        • Contain only digestive enzymes.
      • Secondary:
        • Primary lysosome fuses with food vacuole or organelle.
          • Contain partially digested remnants of other organelles and organic material.
      • Residual body:
        • Contain undigested wastes.
      • Autophagy:
        • Process that destroys worn-out organelles, so that they can be continuously replaced.
      • Apoptosis (programmed cell death):
        • Lysosomes release digestive enzymes into the cell.
    www.freelivedoctor.com
  • 12. Peroxisomes
    • Membrane-enclosed organelles.
      • Contain specific enzymes that promote oxidative reactions.
      • Oxidize molecules and form H 2 0 2 .
    • Catalase: converts H 2 0 2 H 2 0 + 0 2 .
    • Oxidation of toxic molecules by peroxisomes is an important function of liver and kidney cells.
    www.freelivedoctor.com
  • 13. Mitochondria
    • Sites for energy production of all cells; but mature RBCs.
    • Contain own DNA, can reproduce themselves.
    • Structure:
      • Outer membrane: smooth.
      • Inner membrane: cristae.
      • Cristae and matrix compartmentalize mitochondrion space.
        • Have different roles in energy generation.
    www.freelivedoctor.com
  • 14. Ribosomes
    • Protein factories:
      • Proteins produced according to genetic information contained in mRNA.
      • Located in cytoplasm and on the surface of endoplasmic reticulum.
    • rRNA molecules serve as enzymes (ribozymes) required for protein synthesis.
      • Contains 2 subunits composed of rRNA and proteins.
    www.freelivedoctor.com
  • 15. Endoplasmic Reticulum (ER)
    • Granular (rough) ER:
      • Bears ribosomes on surface, in cells active in protein synthesis.
        • Proteins enter cisternae are modified for secretion.
    • Agranular (smooth) ER:
      • Provides site for enzyme reactions in steroid hormone production and inactivation.
      • Storage of Ca 2+ in striated muscle cells.
    www.freelivedoctor.com
  • 16. Golgi Complex
    • Stacks of hollow, flattened sacks with cisternae.
      • One side of sack faces site for entry of vesicles from ER that contain cellular products.
      • Other site faces towards plasma membrane and releases vesicles of chemically modified products.
    • Modifies proteins, separates according to destination, and packages into vesicles.
    www.freelivedoctor.com
  • 17. Cell Nucleus
    • Most cells have single nucleus.
    • Enclosed by inner and outer membrane (nuclear envelope).
      • Outer membrane is continuous with ER.
    • Nuclear pore complexes fuse inner and outer membranes together.
      • Selective active transport of proteins and RNA.
        • Regulation of gene expression.
          • Transport of mRNA out of nucleus to ribosomes.
    • Nucleoli:
      • DNA contains the genes that code for the production of mRNA.
    www.freelivedoctor.com
  • 18. Chromatin
    • DNA within nucleus combines with protein (histones) to form chromatin.
      • Thread-like material that makes up the chromosomes.
      • Histone proteins are positively charged and form spools around which the negatively charged DNA strands wrap.
    • Euchromatin:
      • Active in genetic transcription.
    • Heterochromatin:
      • Contains genes that are permanently inactivated.
    www.freelivedoctor.com
  • 19. Chromatin (continued) www.freelivedoctor.com
  • 20. RNA Synthesis
    • One gene codes for one polypeptide chain.
      • Each gene is several thousand nucleotide pairs long (DNA).
    • Each gene contains the code for the production of a particular type of mRNA.
      • For the genetic code to be translated into synthesis of a particular protein, the DNA code is copied onto a strand of RNA (genetic transcription).
    www.freelivedoctor.com
  • 21. Genetic Transcription
    • RNA-polymerase breaks weak hydrogen bonds between paired bases of DNA.
      • Regulatory molecules act as transcription factors by binding to promoter region of gene, activating the gene.
    • Double stranded DNA separates at region to be translated.
      • One freed strand of DNA serves as guide.
        • Freed bases pair with complementary RNA nucleotide bases.
    • RNA detaches.
    www.freelivedoctor.com
  • 22. Types of RNA
    • 4 types of RNA produced within nucleus by transcription.
      • Precursor mRNA pre-mRNA):
        • Altered in nucleus to form mRNA.
      • Messenger RNA (mRNA):
        • Contains the code for synthesis of specific proteins.
      • Transfer RNA (tRNA):
        • Decodes genetic message contained in mRNA.
      • Ribosomal RNA (rRNA):
        • Forms part of the ribosome structure.
    www.freelivedoctor.com
  • 23. Pre-mRNA
    • Contains excess bases within the pre-mRNA.
    • Introns:
      • Regions of non-coding DNA within a gene.
    • Exons:
      • Coding regions.
    • Introns are removed and the ends of exons spliced by snRNPs to produce mRNA.
    www.freelivedoctor.com
  • 24. Protein Synthesis
    • Each mRNA passes through ribosomes forming a polyribosome.
    • Association of mRNA with ribosomes is needed for genetic translation.
    • Translation:
      • Production of specific protein according to code contained in mRNA base sequence.
    www.freelivedoctor.com
  • 25. Protein Synthesis (continued) www.freelivedoctor.com
  • 26. Protein Synthesis (continued)
    • Each mRNA contains hundreds of nucleotides arranged in sequence determined by the complementary base pairing with DNA.
    • Codon:
      • Each 3 bases (triplet) is a code word for a specific amino acid.
    www.freelivedoctor.com
  • 27. Protein Synthesis (continued) www.freelivedoctor.com
  • 28. Transfer RNA
    • Translation of the codons accomplished by tRNA and enzymes.
      • tRNA bends on itself, making an anticodon (3 nucleotides that are complementary to codon of mRNA).
    • Synthetase enzymes join specific amino acids to the ends of tRNA within a given codon.
    www.freelivedoctor.com
  • 29. Formation of a Polypeptide
    • Anticodons of tRNA binds to mRNA codons.
    • Each tRNA carries a specific amino acid.
      • tRNA bring amino acids close together.
      • Amino acid detaches from tRNA.
        • Enzymatically this amino acid is transferred to the amino acid on the next tRNA.
      • Polypeptide chain grows.
    • Interactions between amino acids cause chain to twist and fold forming secondary and tertiary structure.
    www.freelivedoctor.com
  • 30. Translation of mRNA www.freelivedoctor.com
  • 31. Functions of ER and Golgi Complex
    • Proteins to be secreted by the cell are synthesized by mRNA-ribosome complexes located on granular ER.
      • Proteins enter the cisternae, and are modified.
      • Leader sequence of amino acids is attracted to membranes of ER.
        • Once proteins are in cisternae, the leader sequence is removed.
          • Enzymatic removal of regions in protein, alter structure.
    www.freelivedoctor.com
  • 32. Functions of ER and Golgi Complex (continued)
      • Secretory proteins are transported to Golgi complex.
        • Further modified, packaged in vesicles, and secreted.
    www.freelivedoctor.com
  • 33. DNA Replication
    • DNA is the only molecule in the body capable of replication.
    • DNA helicases break weak hydrogen bonds to produce 2 free strands of DNA.
    • Bases of each of the freed DNA strands can bind to complementary bases.
    • Each copy is composed of one new strand and one strand from the original DNA molecule.
    • Preserves the sequence of bases in DNA.
    www.freelivedoctor.com
  • 34. DNA Replication (continued) www.freelivedoctor.com
  • 35. DNA
    • Law of Complementary Base Pairings:
    • # of purine bases = # pyrimadine bases.
      • Adenine only pairs with thymine.
      • Guanine only pairs with cytosine.
      • DNA polymerases join the nucleotides together to form a second polynucleotide chain.
    www.freelivedoctor.com
  • 36. Cell Cycle
    • Interphase (non-dividing cell phases):
      • G 1 :
        • Produces mRNA and proteins.
      • S:
        • If cell is going to divide, DNA replicated.
      • G 2 :
        • Chromosome consists of 2 chromatids joined by centromere.
        • Each chromatid contains a complete double-helix DNA molecule. Each chromatid will become a separate chromosome once mitotic division completed.
        • Completes interphase.
    www.freelivedoctor.com
  • 37. Cyclins
    • Cyclins promote different phases of the cell cycle.
      • During G 1 phase an increase in cyclin D proteins activates enzymes to move the cell quickly through the G 1 phase.
        • Overactivity of a gene that codes for cyclin D might cause uncontrolled cell division (cancer).
    • Oncogenes:
      • Mutated forms of normal genes that contribute to cancer.
    • Tumor suppressor genes:
      • Inhibit cancer development.
      • Suppressor gene p53 indirectly blocks the ability of cyclins to stimulate cell division.
        • Induces the expression of gene p21, which inactivates the cyclin-dependent kinases.
        • Promotes cell differentiation.
    www.freelivedoctor.com
  • 38. Mitosis (M Phase)
      • Prophase:
        • Chromosomes become visible distinct structures.
      • Metaphase:
        • Chromosomes line up single file along equator.
          • Action of spindle fibers attached to kinetochore
      • Anaphase:
        • Centromeres split apart.
          • Spindle fibers shorten, pulling the 2 chromatids in each chromosome to opposite poles.
      • Telophase:
        • Division of cytoplasm, producing 2 daughter cells.
    www.freelivedoctor.com
  • 39. Mitosis (continued) www.freelivedoctor.com
  • 40. Mitosis (continued) www.freelivedoctor.com
  • 41. Role of Centrosome
    • All animal cells have centrosome, located near nucleus in non-dividing cell.
      • At center are 2 centrioles.
        • Each centriole composed of 9 bundles of microtubules.
          • Microtubules grow out of pericentriolar material.
      • Centrosome replicates itself during interphase (if cell is going to divide).
      • Identical centrosomes move away from each other during prophase.
      • Take up opposite poles by metaphase.
        • Microtubules from both centrosomes form spindle fibers.
          • Spindle fibers pull chromosomes to opposite poles during anaphase.
    www.freelivedoctor.com
  • 42. Telomeres and Cell Division
    • Decreased ability of cells to divide is an indicator of senescence (aging).
      • May be related to the loss of DNA sequences at the ends of chromosomes (regions called telomeres).
        • Telomeres serve as caps on the ends of DNA.
          • Prevent enzymes from mistaking the normal ends for broken DNA.
        • DNA polymerase does not fully copy the DNA at end-regions.
          • Each time a chromosome replicates it loses 50-100 base pairs in its telomeres.
      • Germinal cells can divide indefinitely due to an enzyme telomerase.
        • Duplicates telomere DNA.
    www.freelivedoctor.com
  • 43. Meiosis (Reduction Division)
    • Cell division occurring in ovaries and testes to produce gametes (ova and sperm cells).
    • Has 2 divisional sequences:
      • First division:
        • Homologous chromosomes line up side by side along equator of cell.
        • Spindle fibers pull 1 member of the homologous pair to each pole.
          • Each of the daughter cells contains 23 different chromosomes, consisting of 2 chromatids.
    www.freelivedoctor.com
  • 44. Meiosis (Reduction Division) (continued)
      • Second division:
        • Each daughter cell divides, with duplicate chromatids going to each new daughter cell.
          • Testes: produce 4 sperm cells.
          • Ovaries: produce one mature egg, polar bodies die.
    www.freelivedoctor.com
  • 45. www.freelivedoctor.com
  • 46. Cell Death
    • Pathologically:
      • Cells deprived of blood supply swell, the membrane ruptures, and the cell bursts (necrosis).
    • Apoptosis:
      • Cells shrink, membranes become bubbled, nuclei condense.
    • Capsases (“executioner enzymes”):
      • Mitochondria membranes become permeable to proteins and other products.
    • Programmed cell death:
      • Physiological process responsible for remodeling of tissues during embryonic development and tissue turnover in the adult.
    www.freelivedoctor.com